Detection and location of fluid leaks in underground fluid-conveying pipes is frequently desirable to avoid unnecessary, time-consuming excavations and attendant costs. As a result, the need has arisen for a reliable system which can be employed on the surface above an underground pipe for accurately locating the site of a fluid leak in the pipe before making an excavation.
Numerous leak detecting systems have been proposed prior to this invention, some for merely detecting the presence of a leak, others for both detecting and locating a leak in a fluid-conveying pipeline. Examples of these prior systems are described in U.S. Pat. No. 3,814,207 issued on June 4, 1974 to T. Kusuda et al, U.S. Pat. No. 3,055,209 issued on Sept. 25, 1962 to J. M. Reid et al, U.S. Pat. No. 3,851,521 issued on Dec. 3, 1974 to S. A. Ottenstein, U.S. Pat. No. 3,478,576 issued on Nov. 18, 1969 to T. G. Boyle, U.S. Pat. No. 3,807,220 issued on Apr. 30, 1974 to S. A. Ottenstein et al, U.S. Pat. No. 3,800,217 issued Mar. 26, 1974 to D. A. Lowrance, U.S. Pat. No. 3,750,711 issued on Aug. 7, 1973 to J. T. Conklin et al, U.S. Pat. No. 3,744,298 issued on July 10, 1973 to N. E. Flournoy et al, U.S. Pat. No. 3,738,156 issued on June 12, 1973 to H. Bosselaar, U.S. Pat. No. 3,690,150 issued on Sept. 12, 1972 to J. S. Mullen, U.S. Pat. No. 3,575,040 issued on Apr. 13, 1971 to H. Bosselaar, U.S. Pat. No. 3,561,256 issued on Feb. 9, 1971 to W. M. Bustin et al, U.S. Pat. No. 3,531,264 issued on Sept. 29, 1970 to F. J. Greipel, U.S. Pat. No. 3,530,705 issued on Sept. 29, 1970 to F. M. Lathrop, U.S. Pat. No. 3,508,433 issued on Apr. 28, 1970, U.S. Pat. No. 3,500,676 issued on Mar. 17, 1970 to M. N. Palmer, U.S. Pat. No. 3,462,240 issued on Aug. 19, 1969 to H. Bosselaar et al, U.S. Pat. No. 3,409,897 issued on Nov. 5, 1968 to H. Bosselaar et al, U.S. Pat. No. 3,413,653 issued on Nov. 26, 1968 to F. M. Wood, U.S. Pat. No. 3,321,957 issued on May 30, 1967 to M. Blander et al, U.S. Pat. No. 3,308,424 issued on Mar. 7, 1967 to A. B. Simpkins et al, U.S. Pat. No. 3,261,200 issued on July 19, 1966 to F. V. Long, U.S. Pat. No. 3,192,516 issued on June 29, 1965 to A. B. Simpkins et al, U.S. Pat. No. 3,170,152 issued to F. V. Long on Feb. 16, 1965, U.S. Pat. No. 3,028,450 issued on Apr. 3, 1962 to D. J. Manning, U.S. Pat. No. 3,626,750 issued to C. A. Talman, and U.S. Pat. No. 3,008,934 issued on July 23, 1935 to A. C. Smith. Other prior patents know to applicant, though not describing to fluid leak detecting systems, are U.S. Pat. No. 3,295,362 issued to F. M. Wood et al on Jan. 3, 1967, U.S. Pat. No. 3,753,260 issued on Aug. 14, 1973 to A. Nelkin et al, U.S. Pat. No. 3,756,275 issued on Aug. 21, 1973 to N. G. Carter et al, U.S. Pat. No. 3,264,863 issued on Aug. 9, 1966 to N. Mapopis, and U.S. Pat. No. 3,253,457 issued to W. E. Parkala et al on May 31, 1966.
Of the foregoing prior disclosures, U.S. Pat. Nos. 3,814,207, 3,851,521, 3,478,576 and 3,055,209 are of particular interest. The leak detecting systems described in these patents, however, are disadvantageous for one reason or another.
In U.S. Pat. No. 3,814,207, for example, apparatus for measuring fluid velocity and complex circuitry for performing mathematical operations is required for locating the site of a leak in a pipeline. In U.S. Pat. No. 3,478,576, the apparatus is not capable of locating the site of a fluid leak and requires the insertion of a pig into the pipe to detect a leak. The system described in U.S. Pat. No. 3,055,209 while capable of locating a leak in an underground pipe requires a sound generator to artifically develop a sound for locating the leak. The apparatus in U.S. Pat. No. 3,851,521, on the other hand, is capable of detecting the location of the leak only at the moment of pipeline rupture.